Gary I take off my hat to you Sir - what an absolutely fabulously informative response!! My error was in mixing loop and recs and in trying to use the .3 increments in the loop records - which as you have explained appear to have been subjected to a conversion along the way. Wow - many thanks for the full explanation of just how the calculation was done!!
Andrew On Tuesday, 27 November 2018 06:56:43 UTC+2, gjr80 wrote: > > OK, let's do the maths... > > Assume the default rain window (rain_period) of 900 seconds (15 minutes). > WeeWX will calculate loop rainRate as sum of loop rainfall over the last > 900 seconds * 3600/900. > > First rain event is loop packet at 08:40:27 where 0.11811023622 fell. > Previous rainRate was 0.0 so we know no rain fell in the previous 15 > minutes. weeWX would calculate rainRate as 0.11811023622*3600/900 = > 0.472440945. Log indicates 0.472440944882. > > Loop packets from 08:40:28 to 08:51:15 inclusive have no recorded rainfall > so rainRate remains at 0.11811023622*3600/900 = 0.472440945. Log > indicates 0.472440944882 in each loop packet. > > Loop packet 08:51:40 has a rain event that includes 0.11811023622 > rainfall. weeWX would calculate rainRate as > (0.11811023622+0.11811023622)*3600/900 = 0.94488189. Log indicates > 0.944881889764. > > No further loop rainfall occurs so loop rainRate remains 0.944881889764 > for the rest of the screen capture. Had the screen capture continued and no > further rainfall occurred I would expect loop rainRate would decay to > 0.472440944882 in the first loop packet after 08:55:27. rainRate would > drop to 0.0 in the first loop packet after 09:06:40. > > rainRate in archive records works a little differently, in particular > when software record generation is used (it's not clear what is being used > in this case but I expect it will be software record generation). When > software record generation is used the archive record rainRate is taken > as the average of the loop rainRate values seen during the archive > period. In this case the first archive record at 08:40:00 had seen no rain > and rainRate = 0. The screen capture indicates 0.0 > > The 08:42:00 archive record would have seen loop packets at 08:40:15, > 08:40:27 and 08:40:28 with respective rainRate values of 0, > 0.472440944882 and 0.472440944882. The average of these is > (2*0.472440944882)/3 = 0.31496063. The screen capture indicates 0.31496063. > > The 08:44:00 archive record will have seen the loop rainRate value of > 0.472440944882 seven times. The average being 0.472440944882. The screen > capture indicates 0.472440944882. > > The 08:46:00 archive record saw loop rainRate of 0.472440944882 three > times so the resulting average is 0.472440944882. The 08:48:00 archive > record saw loop rainRate of 0.472440944882 four times so the resulting > average is 0.472440944882. The 08:50:00 archive record saw loop rainRate > of 0.472440944882 once so the resulting average is 0.472440944882. These > values agree with the screen capture. > > The 08:52:00 archive record saw loop rainRate of 0.472440944882 three > times and 0.944881889764 once so the resulting average is 0.590551181102. > The screen capture indicates 0.590551181102. > > The 08:54:00 archive record saw loop rainRate of 0.944881889764 three > times so the resulting average is 0.944881889764. The screen capture > indicates 0.944881889764. > > So the upshot is given the rain values in the loop packets weeWX is > calculating loop and archive rainRate exactly as it should. Where I > believe the error lies is in the loop rain values as mentioned by the OP in > post #3. If we look at the first rain event the rain_total jumps from > 63.0 to 63.3 yet rain is recorded as 0.11811023622; we would have > expected 0.3 ie the simple difference between success rain_total values. > Also, if we multiply 0.11811023622 by 2.54 we get 0.3. So clearly we have a > cm to inches conversion occurring somewhere that is not needed. My quick > look at the SDR driver did not reveal anything, probably needs Matthew's > eye! > > Gary > > > On Tuesday, 27 November 2018 01:49:13 UTC+10, Andrew Milner wrote: >> >> I cant get anything like the given rainrates for the period of the log >> >> A longer log extract is definitely needed!! >> >> >> >> On Monday, 26 November 2018 10:39:48 UTC+2, gjr80 wrote: >>> >>> Hi, >>> >>> What makes you say the rainRate is wrong? By default weeWX calculates >>> rainRate over a 15 minute sliding window, your screen capture covers >>> approximately 16 minutes with at least two rain events so seeing a non-zero >>> rain rate in all packets/records after the first rain event is expected. >>> You can change the window size by setting the rain_period config option in >>> weewx.cnf: >>> >>> [StdWXCalculate] >>> .... >>> [[Calculations]] >>> .... >>> rain_period = xxx >>> .... >>> >>> Where xxx is the rain_period to be used in seconds. You will need to >>> restart WeeWX or do a config reload for the new setting to take effect. >>> >>> Gary >>> >>> -- You received this message because you are subscribed to the Google Groups "weewx-user" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
